Biomechanical changes in the cornea following cataract surgery: A prospective assessment with the Corneal Visualisation Scheimpflug Technology.

IMPORTANCE: Intraocular pressure (IOP) is often reduced following cataract surgery. Postoperative changes in corneal stiffness are likely to be at least partly responsible for any reduction in IOP measured with applanation tonometry. BACKGROUND: To determine the effect of cataract surgery and corneal incision size on corneal biomechanics. DESIGN: Prospective randomized trial. PARTICIPANTS: One hundred prospectively enrolled patients qualifying for cataract surgery. METHODS: Participants were randomized to clear corneal incisions with a 2.20 or 2.85 mm keratome. Corneal Visualisation Scheimpflug Technology (Corvis-ST) tonometry and dynamic corneal response measurements were obtained preoperatively, and 3 mo postoperatively. Multiple regression analysis was completed using R software. MAIN OUTCOME MEASURES: Corvis-ST biomechanical parameters. RESULTS: Ninety-three eyes of 93 patients were included in the final analysis. Mean Corvis-ST biomechanically corrected IOP decreased by 3.63 mmHg postoperatively (95% confidence interval = 2.97-4.35, P ≤ 0.01), and central pachymetry increased by 6.96 µm (4.33-9.59, P ≤ 0.01). Independent of IOP and pachymetry changes, mean (±SE) corneal first applanation stiffness parameter reduced by 9.761 ± 3.729 (P = 0.01) postoperatively. First applanation velocity increased by 0.007 ± 0.002 ms, second applanation velocity increased by 0.012 ± 0.004 ms (P ≤ 0.01), the first applanation deformation amplitude increased by 0.008 ± 0.002 mm (P ≤ 0.01) and the deflection amplitude at highest concavity increased by 0.030 ± 0.069 (P ≤ 0.01). There were no significant differences between different incision size groups. CONCLUSIONS AND RELEVANCE: Corneal stiffness is reduced 3 mo following cataract surgery and is associated with falsely low IOP measurements. This finding may be important for glaucoma patients and in particular when assessing the effectivity of minimally invasive glaucoma surgery devices.

Effect of phacoemulsification incision size on incision repair and remodeling: Optical coherence tomography assessment.

PURPOSE: To characterize the effect of incision size on corneal incision repair and remodeling over 3 months after cataract surgery. SETTING: Department of Ophthalmology, Auckland District Health Board, Auckland, New Zealand. DESIGN: Prospective case series. METHODS: Eyes having routine cataract surgery were randomized to receive 2.20 mm or 2.85 mm uniplanar clear corneal incisions. Anterior segment optical coherence tomography of incision thickness, length, width, gaping, and angle and specular microscopy of endothelial cell density (ECD), polymegathism, and pleomorphism were completed at baseline and 1, 7, 30, and 90 days postoperatively. RESULTS: Each incision group comprised 50 eyes (50 patients). Ninety-nine patients (99%) attended all assessments. The Descemet membrane detachment rate was greater than 50% with 2.20 mm incisions (P = .01). Patients with Descemet membrane detachments had increased endothelial wound gaping, slower visual recovery, and increased corneal thickness at the incision site at all visits (φ = 0.54, P < .01). The 2.20 mm group had greater polymegathism despite no difference in the mean phacoemulsification energy between groups (2.20 mm: 32.3% ± 6.2% [SD]; 2.85 mm: 30.8% ± 6.5%) (P = .02). Ninety days postoperatively, the 2.20 mm group had a lower mean ECD (2195 ± 360 cells/mm2) than the 2.85 mm group (2397 ± 335 cells/mm2) (P = .01). Final visual acuity, gaping, and angles were not significantly different between the groups. CONCLUSIONS: The 2.20 mm wide corneal incisions were more prone to trauma than 2.85 mm incisions during routine cataract surgery. Corneal incisions with signs of trauma were associated with prolonged visual recovery and slower healing postoperatively.